The invention relates to an apparatus and a method for irradiating tumour tissue of a patient by means of an ion beam, in accordance with the independent claims.
The most recently developed ion beam scanning apparatuses and methods, such as those on which, for example, the European Patent Application 98 117 256.2 is based, allow increased precision in the irradiation of deep-lying tumours.
Using those apparatuses and methods, the target volume, such as a tumour of a patient, is broken down into layers of identical range, which layers are then scanned area-wise in a grid pattern using an ion beam. The ion beam is brought into a treatment space in relation to a fixed coordinate system, the spatial angle of an ion beam axis in the treatment space being fixed or emission from different spatial angles being possible by means of a gantry.
In order for the tumour of a patient to be positioned in that fixed coordinate system of the irradiation space, the patient must first be brought into the correct desired position relative to that coordinate system so that the actually irradiated or scanned volume of the ion beam conforms to the planned target volume of the tumour in the patient. It is, moreover, necessary in the case of such known systems for the patient to be maintained in the desired position during irradiation. In order to maintain the desired position, complicated devices such as individually fabricated thermoplastic mask systems are used for fixing the patient in position, in order to adjust the patient with millimetre accuracy before irradiation and to stabilise the patient by means of the mask during irradiation. Using the known apparatuses and methods, it is accordingly possible only to irradiate spatially fixed target volumes such as, for example, tumours in the head and neck region and tumours close to the spinal column, wherein either the head alone is fixed in position by means of a suitable mask or a full body mask stabilises the spinal column.
Irradiation of moving target volumes, for example in the thoracic region, has not hitherto been possible using such methods. For example, breathing movement causes the target volume to be displaced by a few centimetres in the thoracic region and, as a result, the desired millimetre precision is made impossible. It is accordingly impossible to achieve fixing in position with millimetre accuracy when, at the same time, internal movements cause displacement of the target volume in the centimetre range. In addition, movement of the target volume whilst beam scanning is being carried out causes substantial dose non-uniformities.
Whereas it would be possible, in the case where the ions in the ion beam have constant energy, for the relatively fast, area-wise, grid-patterned scanning to follow, in terms of time, the lateral movements of the target volume in the centimetre range, the accelerator is not able to vary the energy sufficiently fast to follow the organ movements in terms of depth, for example as a result of breathing or heartbeat in the thoracic region of a tumour patient.
The problem of the invention is to provide an apparatus and a method for irradiating tumour tissue of a patient by means of an ion beam, wherein the ion beam can be adapted to spatial and temporal change, especially spatial and temporal periodic changes in the target volume, both perpendicular to the beam direction and in terms of depth.
The problem is solved by the subject-matter of the independent claims. Features of preferred embodiments are defined in the dependent claims.
In accordance with the invention, the apparatus for irradiating tumour tissue of a patient by means of an ion beam has a device for deflecting the ion beam for slice-wise and area-wise scanning of the tumour tissue and has an accelerator having an ion beam energy control device for step-wise and depth-wise scanning of the ion beam. In addition, the apparatus has an ion-braking device, which is used as a depth-wise scanning adaptation apparatus for adapting the range of the ion beam and which has faster depth-wise adaptation than the energy control device of the accelerator. Furthermore, the apparatus has a movement detection device for detecting a temporal and positional change in the location of the tumour tissue in a treatment space and has a control device which controls the deflecting device and the depth-wise scanning adaptation apparatus for adjustment of the ion beam direction and ion beam range, respectively, when scanning the tumour tissue in the event of temporal and positional change in the location of the tumour tissue in the treatment space.
The apparatus according to the invention has the advantage that moving target volumes of a patient who is moving can be irradiated with the same precision as non-moving target volumes in a patient who is fixed in position. For that purpose, the movement detection device detects the movements of the patient during irradiation, and the irradiation points are correspondingly corrected with the aid of a control device. In principle, it is no longer necessary, in the case of this apparatus, for the patient to be initially adjusted with millimetre accuracy in the fixed spatial coordinates because, with the aid of the movement detection device, the actual initial location of a patient can also be adapted to the treatment program and/or the treatment program corrected accordingly.
In a preferred embodiment of the invention, the apparatus has two electromagnets, by means of which the deflecting apparatus makes possible area-wise scanning. The electromagnets deflect the ion beam orthogonally to the ion beam axis in an X direction and a Y direction, which are, in turn, perpendicular to one another, in order to provide area-wise scanning of the tumour tissue which, relative to depth-wise scanning by means of the ion beam energy control device, is fast. For that purpose, the electromagnets are controlled by fast-reacting power units and measurement devices. Those devices can accordingly also be used to carry out correction and adaptation when scanning tumour tissue in the case of temporal and positional change in the location of the tumour tissue in the treatment space orthogonally to the ion beam axis.
In a preferred embodiment of the invention, the apparatus has at least one accelerator, by means of which the energy of the ion beam is adjustable so that the tumour tissue can be irradiated slice-wise, staggered in terms of depth. That is associated with the advantage that the entire tumour tissue can be successively scanned slice-wise, the range of the ion beam being adjustable from slice to slice by modifying the energy of the ion beam. For that purpose, the accelerator consists essentially of a synchrotron or a synchrocyclotron, in which ions of equal mass and equal energy can be accelerated step-wise to higher energies. Because of the complexity of the control functions for the accelerator, the energy of the ion beam cannot be adapted to specified ranges within the irradiation space or within the tumour volume sufficiently quickly or with the requisite precision for it to be possible to follow the movements of the tumour tissue, or patient, automatically.
In a preferred embodiment of the invention, the depth-wise scanning adaptation apparatus therefore has two ion-braking plates of wedge-shaped cross-section, which cover the entire irradiation field of the ion beam and allow fast depth-wise scanning adaptation in the case of moving tumour tissue.
For that purpose, in a preferred embodiment of the invention, the ion-braking plates are arranged on electromagnetically actuatable carriages. With the aid of those electromagnetically actuatable carriages, the position of the wedge-shaped ion-braking plates can be changed within milliseconds and, accordingly, the length of the braking path of the ions provided in an overlap region of the wedge-shaped braking plates can be varied by the ion-braking plates. For that purpose, the ion-braking plates overlap in the entire irradiation field of the ion beam and can accordingly adapt the ions in terms of their range, irrespective of their position, to positional and temporal changes in a moving target volume.
In a preferred embodiment of the invention, the ion-braking plates are mounted on linear motors. Such linear motors have the advantage that continuous, fine regulation of ion braking is possible for adaptation of depth-wise scanning of the target volume. Changing the position of the wedge-shaped ion-braking plates with the aid of linear motors is, moreover, not only extremely precise positionally but is also adaptable with extreme speed of reaction to temporal change in the target volume in terms of depth.
In a further embodiment, a water-filled cylinder of variable thickness is used instead of the wedges. The covers of the cylinder are made from transparent plates, for example from two plexiglass or silica glass panes, the upper pane of which is moved by 2 or 4 high-performance linear motors. The side covering of the cylinder is in the form of a bellows made from steel or rubber. Variation of the thickness of the water layer is assisted by a hydraulic system which, when the cylinder is drawn apart, pumps water into the cylinder and, when it is pressed together, draws water out so that the drive is spared and the formation of vacuoles is prevented.
This embodiment has the advantage that a smaller minimum thickness is possible than in the case of the wedges. In the case of the wedges, the minimum thickness is calculated from the wedge slopexc3x97field size (typically 5 cm). In the case of the cylinder arrangement, the minimum thickness is given by the thickness of the two covers (typically 1 cm). That small minimum thickness reduces the beam scatter and accordingly improves the beam quality. The cylinder arrangement is, moreover, more compact than the wedge construction in the transverse direction.
In a further preferred embodiment of the invention, the movement detection device has at least two measurement sensors which, from two spatial angles in relation to an ion beam axis, detect the temporal and positional location of markings on a region of the body of a patient containing tumour tissue. Such markings can be applied using skin-compatible luminous colours in the form of dots, dashes or other geometric shapes or in the form of luminous elements so that they can be clearly detected and measured by the measurement sensors.
In a further preferred embodiment of the invention, the measurement sensors are precision video cameras, which co-operate with an image-evaluating unit. By that means it is advantageously possible for the movements of a region of the body in the vicinity of tumour tissue to be exactly measured and correlated to the temporal and positional changes in the location of the tumour tissue.
Alternatively to the movement detection system which uses markings on the surface of the body and a precision video camera, a further embodiment of the invention has an X-ray system, which detects the movements of the tumour tissue directly in the body. In the case of that movement detection system, two X-ray tubes are mounted with their beam directions orthogonal to the ion beam. The two X-ray tubes are, in turn, also oriented perpendicular to one another. In addition, two sensitive X-ray image intensifiers are in each case mounted opposite, on the other side of the patient. The X-ray tubes emit short X-ray flashes of low power, in order to keep the dosage low, at a frequency of, for example, 20 Hz. The associated X-ray images are recorded by the image intensifiers and digitised. As a result, an image sequence for two directions is obtained, from which, using a suitable method and appropriate software, the displacement of the target points P1 is determined in virtually real time with a delay of approximately 50 ms.
That embodiment has the advantage that much more information on movements in the interior of the body is obtained from the X-ray recordings than from external markings on the surface of the body, allowing more precise determination of temporal and positional organ displacements.
In principle, irradiation of the tumour volume is made up from image points, which are set beside one another area-wise in a grid pattern in the form of a slice, the ion beam being deflected from scanning point to scanning point orthogonally to its beam axis in an X direction and a Y direction. Even though the energy of the ions in an ion beam can be kept constant by the accelerator in question, the number of ions per volume point is not constant over time. In order, nevertheless, to beam an ion beam dose of equal magnitude into every volume point of the tumour tissue, an ionisation chamber having a fast read-out for monitoring the intensity of the ion beam flow is, in a preferred embodiment of the invention, arranged as a transmission counter in the beam path of the ion beam. Such a transmission counter determines the dwell time of the ion beam at a volume point being irradiated in the tumour volume, and a control unit connected thereto diverts the ion beam to the next volume point as soon as a specified beam dose has been achieved. It is, consequently, advantageously possible to scan a volume slice of a tumour volume area-wise in a grid pattern.
The ionisation chamber is preferably arranged between the deflecting device and the depth-wise scanning adaptation apparatus, especially as the depth-wise scanning adaptation apparatus having its wedge-shaped braking plates or the water layer between transparent plates merely controls the ions in terms of their range without, however, influencing the ion dose.
A method of irradiating tumour tissue of a patient by means of an ion beam comprises the following method steps:
placing the patient on an apparatus matched to the contour of the patient for the purpose of positioning the patient in an irradiation space,
applying markings to a region of the body of the patient, close to the tumour tissue,
determining the temporal and positional change in the markings by means of a movement detection device or capturing X-ray images of the tumour tissue from two mutually perpendicular directions of X-ray beams orthogonal to the ion beam,
adjusting the ion beam, whilst scanning the tumour tissue using an ion beam deflecting device and an ion beam energy control device, by means of an additional depth-wise scanning adaptation apparatus, which adapts the range of the ion beam to the temporal and positional changes in the markings, determined by the movement detection device, in co-operation with the ion beam deflecting device.
Using that method, it advantageously becomes possible to achieve the same precision in the millimetre range when irradiating moving tumour volumes in a patient who is moving as in the case of the patient who is fixed in position, even when the tumour tissue moves up to several centimetres periodically, for example as a result of heartbeat or breathing air. In this method, ion beam irradiation continuously follows the temporal and positional change in the location of the tumour tissue and it is not necessary to delay the irradiation until a repeating positional location has been achieved. Slow movements of the patient that occur on a non-periodic basis are also allowable and ion irradiation thereof can, with the aid of the depth-wise adaptation apparatus and the deflecting device, be adapted temporally and positionally. Only in the case of sudden changes in location such as fits of coughing does the irradiation procedure have to be suspended.
Compared to methods that allow irradiation only when identical locations of the tumour tissue have been achieved, the method according to the invention has the advantage that the irradiation time for a patient can be significantly shortened because the irradiation procedure is not dependent on, for example, the periodicity of the heartbeat or of the breathing of a patient.
Further advantages and features of the present invention will be described below in further detail with respect to embodiments with reference to the accompanying drawings.